1. Technical Field
The present invention relates to a power assist device that assists the travel of a vehicle driven by human strength and to an ambulatory assist vehicle having the power assist device that assists the walking of an operator.
2. Background Art
An ambulatory assist vehicle such as a handcart, a wheelchair, a pushcart and the like is made so as to move (travel) when an operator pushes on a grip part. In recent years, this type of ambulatory assist vehicle has a power assist function internally that assists walking using output torque from an electric motor. The ambulatory assist vehicle with this type of power assist function has a sensor for detecting input (operating force) from a hand of the operator in the grip part provided on the ambulatory assist vehicle. Furthermore, it has a control unit for controlling the electric motor so as to output the power assist force determined based on the operating force from the operator as detected by the sensor.
For example, in the power assist walking device described in Patent Reference 1, when an input value detected by a sensor is a maximum value that is a fixed fluctuation value (first fluctuation value) or less, it is determined that the power assist walking device has moved at the same speed as the operator. Furthermore, power assist is performed using an output value that is proportional to a reference value given based on the maximum value of the input value. Additionally, when the absolute value of the difference between the input value and the reference value is a separately determined difference value (second fluctuation value), that input value newly replaces the reference and is used to perform power assist. By performing power assist in this way, the power assist walking device can be made to travel smoothly in accordance with the walking speed of the operator.